Revertible draft fluid-fuel-burning heater with safety pilot draft



June 5, 1956 J o V ETAL REVERTIBLE DRAFT FLUID-FUEL-BURNING HEATER WITH SAFETY PILOT DRAFT Filed March 22, 1952 Imventorsz JAMES O. IVIE, v MQYER D THOMAS; fiaawwmw XI ttornegs.

United States Patent REVERTIBLE DRAFT FLUID-FUEL-BURNING HEATER WITH SAFETY PILOT DRAFT James O. Ivie and Meyer D. Thomas, Salt Lake City, Utah Application March 22, 1952, Serial No. 278,016

2 Claims. (Cl. 158-1) This invention relates to revertible draft fluid-fuelburning heaters.

The principal objects of the invention are to provide safety, reliability, economy, automatic operation and simplicity of construction for down draft heaters using gas or other fluid fuel.

Additional objects appear hereinafter.

Heaters which burn fluid fuel, such as ordinary gas, have main burners for heating, and pilot burners for insuring ignition of the main burners. Pilot burners must have constant burning characteristics, while main burners function intermittently. A dependable pilot burner is in fact, a safety device for the main burner.

For efficiency, main burners are usually operated under forced draft. Pilot burners, on the contrary, usually operate under natural draft.

Gas heaters based on the principle of down draft or counterflow draft are known to be highly efficient, but heretofore have lacked simplicity in construction and operation when used with pilot burners.

A feature of the invention is to cause a revertible draft fluid-fuel-burning heater to be automatically switched from main burner forced draft to pilot burner natural draft, or vice versa, without the use of mechanical means such as dampers.

According to the invention, a forced draft circuitous conduit and a natural draft direct conduit extend independently of each other, from a combustion chamber to a waste flue in common. The amount of fluid which passes through the forced draft conduit in unit time is much greater than is the amount which passes through the natural draft conduit. The exact ratio between the two rates of flow depends upon individual conditions and is controlled.

Under forced draft operation the total fluid flow from burners may be caused to divide itself quantitatively as it leaves the combustion chamber, into two streams which are substantially in proportion to each other in accordance with the flow capacities of the respective conduits.

Cutting off the forced draft, automatically causes all of the pilot burner waste gases to pass out under natural draft. Restoring forced draft causes the waste gases from both burners to pass out under forced draft. All this is accomplished without the aid of mechanically operated devices.

Because of the forced draft, the current of gases passing through the waste flue may be used, if desired, to induce an aspiratory effect in the natural draft conduit for augmenting the effect of the natural draft. The extent of the aspiratory effect is controlled by properly shaping the outlet mouth or nozzle of the natural draft conduit where it enters the waste flue, in accordance with well known principles of nozzle design. An upward surge of the burning gases in the combustion chamber influences the pressure in the natural draft conduit. Finally, a restrictive pressure is asserted in that conduit, if desired, by modifying the aforesaid nozzle design.

In the accompanying drawing,

Fig. 1 represents an elevation, partially in vertical section, of a properly equipped revertible draft heater;

Fig. 2, a diagram indicating the normal flow of air and fuel through the heater, and the resulting normal discharge of the waste combustion products;

Fig. 3, a diagram similar to Fig. 2, but showing the gravity flow of waste gases from the pilot light only, as automatically switched directly into the waste flue, if and when there is interference with the normal artificial draft.

Referring to the drawing, the numeral 10 denotes a shell having a tightly walled dome 10a which encloses a combustion chamber 11, the latter being located above a main burner 12 using combustible fluid. The main burner is located in a base compartment or firebox 13, and is positioned below the combustion chamber 11, so as to be in the path of the incoming air draft indicated by the arrows 14. The base compartment or firebox 13 is preferably spaced upwardly of a floor surface 15 and is suitably supported, for example by legs 16, so as to provide ample space for the passage of the incoming air.

In the present instance, a helically coiled pipe or conduit 17 extends from an outlet 18 in the upper part of the combustion chamber 11 downwardly on the outside of the combustion chamber wall, to an outlet branch 19. The branch 19 is directly connected to the intake opening 29 of a suction fan 21. The discharge 22 from the suc tion fan 21 flows into a waste flue 23, which latter may lead into the atmosphere.

In the diagrams, Figs. 2 and 3, the revertible draft coil 17 is shown at one side of the combustion chamber 11, instead of extending around the latter as set forth in Fig. 1. This is merely for the sake of clarity.

Gas, oil or other fuel is supplied to the main burner 12 through a supply pipe 24 which may be controlled by a usual valve 25. A branch 26 leads from any suitable point in the supply pipe to a pilot burner 27. The pilot burner 27 is located in close proximity to the main burner 12 so as to be ready to relight the fuel at the main burner whenever necessary.

Since a pilot burner is not utilized essentially for heating, it is desirable from the standpoint of economy, to allow it to consume only a necessary minimum of fuel. In other words it is desirable to limit the amount of heat necessary to maintain sufiicient draft to keep the pilot flame alive, to an extent commensurate with the heat supplied by the pilot burner itself.

A further purpose in restricting the natural draft conduit is to prevent changing weather conditions from creating draft surges which otherwise would extinguish the pilot flame. Therefore it is also desirable to restrict to a minimum the flow capacity of the natural draft conduit leading from the pilot burner, so as not to dissipate unduly the relatively small amount of heat available to maintain circulation of fluid in that conduit. This is here accomplished by providing a natural draft conduit 28 of minimum size for the pilot burner 12, and leading the conduit 28 as directly as possible into the waste flue 23.

As an inventive feature, the natural draft conduit 23 is separate and distinct throughout its length, from the forced draft conduit 19. The two conduits are widely spaced apart from each other structurally so any heat exchange between the two is impossible. It is further to be observed that the natural draft conduit 28 is fully open constantly, there being no obstruction at any time. This is possible without loss of efliciency by reason of the small size of the flow passage of conduit 28 relative to the sizes of the flow passages of revertible draft conduit 19 and natural draft waste flue 23, respectively, and of the blocking action of the relatively higher pressure in waste flue 23 during normal operation, considering the forced draft 3 condition therein. Thus, efficiency is achieved without any need for mechanical dampers.

Assuming that the apparatus of the invention is functioning under natural draft, then the stream 29 of heated combustion products from the pilot burner 27 ascends and flows as at 30, into the restricted conduit 23. Subsequently, this stream at 31 enters the waste flue 23.

Now, assuming that the functioning is under forced draft, then the gases from both the pilot burner and the main burner mix, indicated by the ascending stream arrows 32 in Fig. 2. The mixed stream divides, the greater portion passing out at 18 to follow through the forced draft conduit 19. Still under forced draft, a much smaller portion of the mixed stream passes at 30a into restricted conduit 28, and at 310, enters the waste flue 23.

As shown in Fig. l, the upper part of combustion chamber 11, the natural draft conduit 28 and the waste flue 23, preferably form a self-contained, air-tight assembly, which simplifies construction and reduces manufacturing costs.

Obviously, this heater is adaptable to requirements of different kinds, such for example, as hot air furnaces, steam boilers and so on. In the drawing only the bare heater is illustrated.

Satisfactory Pitot tube tests have been conducted with heaters of the invention, which show no loss in efficiency by reason of using the conduit 28, open, instead of closing the same during forced draft operation. This proves there is no need for dampers or other mechanical regulating devices.

Briefly, the purpose of the invention is to provide forced revertible draft means adapted to normally carry-off the major portion of mixed combustion gases from a main burner and a pilot burner. Further, to provide natural up-draft conduit means which is perpetually open throughout, from the two burners to the atmosphere, and normally is restricted to carry off the minor portion of the combustion gases from the pilot burner. And finally, to provide revertible draft conduit means which is operatively associated with forced draft means, so as at one time to be effective to draw combustion gases through only the revertible draft conduit means, and at another time, to cause the combustion gases from the pilot burner to be drawn wholly into and through the natural up draft con- What is claimed is:

l. A revertible draft, fluid-fuel-burning heater with safety pilot draft, comprising a main burner; a pilot burner in cooperative conjunction with the main burner; cornbustion chamber means enclosing the two said burners and having a closed dome; forced revertible draft means having an intake below the dome for combustion gases; a waste flue leading from the revertible draft means remote from said dome; and an independent by-pass conduit having an intake below said dome and an outlet in the waste ilue, the passage through the by-pass conduit being small with respect to the passage through the revertible draft means and the passage through the waste flue, and the intake of the by-pass conduit being spaced apart from the intake of the forced revertible draft means.

2. A revertible draft, fluid-fuel-burning heater with safety pilot draft, comprising wall means defining a combustion chamber; a main burner within said chamber; a pilot burner within said chamber in igniting relation with said main burner; a natural up draft waste flue remote from said chamber; forced revertible draft conduit means leading from said chamber into said waste flue, said revertible draft conduit means and said waste flue having flow capacity adapted to carry off, under forced draft conditions, combustion gases from both said burners; forced draft means connected to said revertible draft conduit means for the purpose of normally forcing combustion gases downwardly thercthrough and up said waste flue; and natural draft conduit means independent of the said revertible draft conduit means and leading from said chamber and into said waste flue on the outlet side of said forced draft means, said natural draft conduit means being constantly open and unobstructed and restricted in flow capacity approximately to that required to carry otf combustion gases from the pilot burner, the fiow cross'seetion of said natural draft conduit being small relative to the flow cross-sections of said waste flue and said revertible draft conduit, respectively.

References Cited in the file of this patent UNITED STATES PATENTS 1,224,700 Atherton May 1, 1917 1,674,2l3 McDowell June 19, 1928 1,943,053 Boisset Jan. 9, 1934 2,022,835 Whiteley Dec. 3, 1935 2,376,171 Mueller May 15, 1945 2,504,315 Feuerfile Arp. 18, 1950 FOREIGN PATENTS 63,057 Switzerland Jan. 14, 1913 

